FIG. 1 shows the original structure of a TSV wafer 1, which comprises an integrated circuit layer 11, a silicon wafer layer 12 arranged on integrated circuit layer 11, and conductive materials 13. Conductive materials 13 are buried in silicon wafer layer 12, are approximately perpendicular to surface 121 of silicon wafer layer 12, and connect to integrated circuit layer 11. Generally, end surfaces 131 of conductive materials 13 in an unpolished TSV wafer are about a couple hundred micrometers from surface 121 of silicon wafer layer 12.
Surface 121 is subsequently polished by grinding, so that silicon wafer layer 12 is rapidly thinned, and thereby the distance between end surfaces 131 of conductive materials 13 and surface 121 of silicon wafer layer 12 is reduced to about tens of micrometers or more.
After grinding and thinning silicon wafer layer 12, a damaged layer 14 is formed near surface 121 as shown in FIG. 2. Therefore, after the grinding step, surface 121 should be subjected to fine polishing with a chemical mechanical polishing (CMP) to finish and remove damaged layer 14, and further polish TSV wafer 1 to the desired status.
The ideal status of the finely polished TSV wafer 1 is varied upon the requirements for the subsequent processes. For example, end surfaces 131 of the conductive materials 13 and top surface 121 of silicon wafer layer 12 surrounding thereof are coplanar as shown in FIG. 3, or end surfaces 131 are protruding out of top surface 121 as shown in FIG. 4.
In practical operation, when a TVS wafer is subjected to a CMP process, the silicon wafer layer 12 and the conductive materials 13 are generally polished simultaneously. Thus, for manufacturers who need to polish a substantial amount of TSV wafers, if both the silicon wafer layer 12 and the conductive materials 13 can be simultaneously and rapidly removed to a suitable status, it may save a very considerable working-hour cost in the manufacturing process. However, the commercially available polishing compositions are mainly designed for common silicon wafers composed of only one single material, either silicon or a conductive material, and are not suitable for directly polishing a TSV wafer.
U.S. Pat. No. 4,169,337 is directed to a polishing composition for a silicon wafer comprising colloidal silicon oxide (SiO2) abrasive particles or silica gel, and water-soluble amine. U.S. Pat. No. 5,230,833 is directed to another polishing composition for a silicon wafer comprising colloidal silicon oxide abrasive particles, an organic base and a bactericide. Currently, it is the view of industry that a polishing composition comprising silicon oxide abrasive particles and an organic amine has a significant polishing effect on silicon.
U.S. Pat. No. 5,225,034 is directed to a polishing composition for a conductive material comprising silver nitrate (AgNO3), a solid abrasive material, and an oxidizing agent selected from the following agents: hydrogen peroxide (H2O2), hypochlorous acid (HOCl), potassium hypochlorite (KOCl) or acetic acid (CH3COOH). In general, the polishing compositions for the conductive material commonly used in the industry usually comprise an acidic compound and an oxidizing agent to exhibit a significant polishing effect on the conductive material.
The polishing compositions mentioned above are suitable for polishing a specific single substance such as silicon or a conductive material. When simultaneously polishing silicon and conductive materials, the removal rates for the two substances are very different from each other, and therefore, it is difficult to increase the polishing rates for silicon and the conductive material simultaneously by increasing the amount of one specific ingredient in the polishing composition. For example, when increasing ethylenediamine concentration in the polishing composition, the silicon removal rate significantly exceeds the conductive material removal rate. That is, the silicon removal rate may be higher than 10,000 Å/min while the conductive material removal rate may only be about 1,000 Å/min.
Similarly, the oxidizing agent hydrogen peroxide widely used in the polishing composition may be useful for polishing the conductive materials; however, it may easily oxidize silicon to hard silica. Therefore, when increasing the amount of hydrogen peroxide in the polishing composition, the conductive material removal rate is also increased but the silicon removal rate decreases significantly.
Accordingly, hydrogen peroxide is not considered to be suitable as an ingredient of the polishing composition for simultaneously polishing silicon and a conductive material. There is need for a polishing composition for use in the semiconductor industry that is suitable for polishing a TSV wafer comprising both silicon and a conductive material and can also rapidly and simultaneously remove the silicon and the conductive material on the TSV wafer to be polished (particularly at rates of at least 6000 Å/min for both silicon and conductive material). In addition, the components of the polishing composition should be easily available. A relative polishing method should also be provided.